Pharmacologic Approaches to Improve Mitochondrial Function in AKI and CKD

CKD Due to a Novel Mitochondrial DNA Mutation: A Case Report

In human kidney disease, mitochondrial ultrastructural damage has long been recognized. Although the extent to which such mitochondrial changes contribute to human kidney disease is uncertain, experimental studies clearly demonstrate that mitochondrial damage can instigate pathogenetic processes that drive ongoing kidney disease. Clinical credence for this experimentally based hypothesis is provided by the development of kidney disease in patients with primary mitochondrial disorders. In this regard, substantial interest surrounds the occurrence of kidney disease in primary mitochondrial cytopathies, a heterogeneous group of conditions in which mutations in mitochondrial DNA (mtDNA) or nuclear DNA impair the functionality of components of the mitochondrial respiratory chain. We describe a novel mtDNA mutation in a patient who developed chronic kidney disease. The patient exhibited mitochondrial abnormalities in both muscle and kidney, chronic tubulointerstitial changes, and recurrent episodes of rhabdomyolysis. We outline mechanisms that may underlie the occurrence of chronic kidney disease in the setting of this novel mtDNA mutation. We also underscore the need to consider in relevant kidney diseases the presence of an underlying mitochondrial cytopathy because the latter more commonly exists than is generally recognized.

Renal tubules transcriptome reveals metabolic maladaption during the progression of ischemia-induced acute kidney injury

Renal tubular epithelial cells (TECs) play a critical role in driving acute kidney injury (AKI) progression, but the key molecular features in TECs during this process is not clear. To better understand the molecular characteristics in renal TECs during AKI and renal fibrogenesis, an irreversible AKI mouse model induced by ischemia/reperfusion injury (IRI) was used in this study. The renal tubules were isolated and tubule specific transcriptome was detected by RNA-seq at different stages in the progression of AKI in this model. The overall transcriptome indicated injury and repair process of TEC after renal IRI. In addition, metabolism maladaption was observed during AKI progression to chronic fibrosis. Particularly, we found dysregulation of multiple steps of lipid metabolism in tubule transcriptomes. Oil red O staining revealed massive lipid droplets accumulation in TECs at day 10, thus confirming the defect of lipid metabolism. This is the first study to charaterize renal tubule specific transcriptome during AKI progression. The results shed light on the molecular features in TECs for progressive AKI.

Defining the short-term effects of pharmacological 5'-AMP activated kinase modulators on mitochondrial polarization, morphology and heterogeneity

Background

Under aerobic growth conditions, mitochondria are the major producers of cellular ATP and crucial for the proper performance of organs and tissues. This applies especially to cells with high energy demand, such as the renal proximal tubule epithelium. Mitochondrial dysfunction contributes to the pathology of human health conditions, including various kidney diseases. The improvement of mitochondrial function ameliorates some of these pathologies. This can potentially be achieved with pharmacological compounds. For example, long-term treatment with activators of 5'-AMP activated kinase (AMPK) enhances mitochondrial biogenesis. However, pharmacological damage control during acute cell injury requires that the short-term effects of these compounds and the impact on healthy cells are also understood. It was our objective to define the changes elicited by established modulators of AMPK activity in healthy renal proximal tubule cells.

Methods

Our work combines confocal microscopy with quantitative image analysis, 3D image reconstruction and Western blotting to provide novel insights into the biology of mitochondria. Specifically, we evaluated the effects of pharmacological AMPK modulators (compound C, AICAR, phenformin, resveratrol) on mitochondrial polarization, morphology and heterogeneity. Microscopic studies generated information at the single cell and subcellular levels. Our research focused on LLC-PK1 cells that are derived from the renal proximal tubule. Mitochondrial heterogeneity was also examined in MCF7 breast cancer cells.

Results

Pharmacological agents that affect AMPK activity in renal proximal tubule cells can alter mitochondrial organization and the electrochemical potential across the inner mitochondrial membrane. These changes were compound-specific. Short-term incubation with the AMPK inhibitor compound C caused mitochondrial hyperpolarization. This was accompanied by mitochondrial fragmentation. By contrast, AMPK activators AICAR, phenformin and resveratrol had little impact. We further show that the biological properties of mitochondria are determined by their subcellular location. Mitochondria at the cell periphery displayed higher MitoTracker/Tom70 values as compared to organelles located in the vicinity of the nucleus. This was not limited to renal proximal tubule cells, but also observed in MCF7 cells. Pharmacological AMPK modulators altered these location-dependent properties in a compound-specific fashion. While the region-dependent differences were enhanced with phenformin, they were ameliorated by resveratrol.

Discussion

We evaluated the rapid changes in mitochondrial characteristics that are induced by pharmacological AMPK modulators. Our research supports the concept that pharmacological agents that target AMPK can rearrange mitochondrial networks at the single cell level. Collectively, these insights are relevant to the development of proper strategies for the short-term adjustment of mitochondrial performance.

Control release of mitochondria-targeted antioxidant by injectable self-assembling peptide hydrogel ameliorated persistent mitochondrial dysfunction and inflammation after acute kidney injury

Persistent mitochondrial injury occurs after acute kidney injury (AKI) and mitochondria-targeted antioxidant Mito-2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) (MT) has shown benefits for AKI, but its efficiency is limited by short half-life and side effect in vivo. Self-assembling peptide (SAP) hydrogel is a robust platform for drug delivery. This study aims to develop an SAP-based carrier to slow release MT for enhancing its long-term therapeutic potency on AKI. The KLD with aspartic acid (KLDD) was designed. The microstructure and in vitro release of MT was assayed. The protective role of MT-loaded SAP (SAP-MT) hydrogel on renal mitochondrial injury, tubular apoptosis, and inflammation was evaluated in mice at five days after ischemia-reperfusion injury (IRI). Our results showed that KLDD could self-assemble into cross-linked nanofiber hydrogel and it had lower release rate than free MT and KLD hydrogel. Compared to IRI and free MT mice, SAP-MT mice exerted reduced renal mitochondria-produced ROS (mtROS) and improved mitochondrial biogenesis and architecture. Consequently, SAP-MT mice showed less renal tubular cell apoptosis, kidney injury marker kidney injury molecule-1 (Kim-1) expression, lower level of pro-inflammatory factors expression, and macrophages infiltration than those of IRI and free MT mice. This study suggested that SAP-MT ameliorated IRI due to its extended mitochondrial protection role than free MT and thus improved the long-term outcomes of AKI.

Enhancing Mitochondrial Health to Treat Hypertension

PURPOSE OF REVIEW

This review summarizes literature pertaining to the dawning field of therapeutic targeting of mitochondria in hypertension and discusses the potential of these interventions to ameliorate hypertension-induced organ damage.

RECENT FINDINGS

In recent years, mitochondrial dysfunction has been reported as an important contributor to the pathogenesis of hypertension-related renal, cardiac, and vascular disease. This in turn prompted development of novel mitochondria-targeted compounds, some of which have shown promising efficacy in experimental studies and safety in clinical trials. In addition, drugs that do not directly target mitochondria have shown remarkable benefits in preserving these organelles in experimental hypertension. Enhancing mitochondrial health is emerging as a novel feasible approach to treat hypertension. Future perspectives include mechanistic experimental studies to establish a cause-effect relationship between mitochondrial dysfunction and hypertension and further clinical trials to confirm the reno-, cardio-, and vasculo-protective properties of these compounds in hypertension.

Mitochondrial bioenergetics, redox state, dynamics and turnover alterations in renal mass reduction models of chronic kidney diseases and their possible implications in the progression of this illness

Nowadays, chronic kidney disease (CKD) is considered a worldwide public health problem. CKD is a term used to describe a set of pathologies that structurally and functionally affect the kidney, it is mostly characterized by the progressive loss of kidney function. Current therapeutic approaches are insufficient to avoid the development of this disease, which highlights the necessity of developing new strategies to reverse or at least delay CKD progression. Kidney is highly dependent on mitochondrial homeostasis and function, consequently, the idea that mitochondrial pathologies could play a pivotal role in the genesis and development of kidney diseases has risen. Although many research groups have recently published studies of mitochondrial function in acute kidney disease models, the existing information about CKD is still limited, especially in renal mass reduction (RMR) models. This paper focuses on reviewing current experimental information about the bioenergetics, dynamics (fission and fusion processes), turnover (mitophagy and biogenesis) and redox mitochondrial alterations in RMR, to discuss and integrate the mitochondrial changes triggered by nephron loss, as well as its relationship with loss of kidney function in CKD, in these models. Understanding these mechanisms would allow us to design new therapies that target these mitochondrial alterations.

Ischemia/reperfusion-associated tubular cells injury in renal transplantation: Can metabolomics inform about mechanisms and help identify new therapeutic targets?

Tubular cells are central targets of ischemia-reperfusion (I/R) injury in kidney transplantation. Inflammation and metabolic disturbances occurring within these cells are deleterious by themselves but also favor secondary events, such as activation of immune response. It is critical to have an in depth understanding of the mechanisms governing tubular cells response to I/R if one wants to define pertinent biomarkers or to elaborate targeted therapeutic interventions. As oxidative damage was shown to be central in the patho-physiological mechanisms, the impact of I/R on proximal tubular cells metabolism has been widely studied, contrary to its effects on expression and activity of membrane transporters of the proximal tubular cells. Yet, temporal modulation of transporters over ischemia and reperfusion periods appears to play a central role, not only in the induction of cells injury but also in graft function recovery. Metabolomics in cell models or diverse biofluids has the potential to provide large pictures of biochemical consequences of I/R. Metabolomic studies conducted in experimental models of I/R or in transplanted patients indeed retrieved metabolites belonging to the pathways known to be particularly affected. Interestingly, they also revealed that metabolic disturbances and transporters activities are in very close mutual interplay. As well as helping to select diagnostic biomarkers, such analyses could also contribute to identify new pharmacological targets and to set up innovative nephroprotective strategies for the future. Even if various therapeutic approaches have been evaluated for a long time to prevent or treat I/R injuries, metabolomics has helped identifying new ones, those related to membrane transporters seeming to be of particular interest. However, considering the very complex and multifactorial effects of I/R in the context of kidney transplantation, all tracks must be followed if one wants to prevent or limit its deleterious consequences.